Inkjet recording apparatus

ABSTRACT

An inkjet recording apparatus of the present invention includes: a drum which conveys a recording medium, a wiper extended in the axial direction of the drum, and inkjet heads aligned in the circumferential direction of the drum along the outer circumferential surface of the drum. The inkjet heads are moved by a head-moving mechanism to be in a recording position or a wiping position. The wiper-moving mechanism moves the wiper in the circumferential direction along the outer circumferential surface so that the wiper wipes ejection surface of at least one of the inkjet heads while the inkjet heads are in the wiping position.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. 2007-199905, which was filed on Jul. 31, 2007, the disclosure ofwhich is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inkjet recording apparatus whichejects ink droplets to record an image on a recording medium.

2. Description of the Related Art

Japanese Unexamined Patent Publication No. 59597/2005 (Tokukai2005-59597) discloses an inkjet printer including a conveyance mechanismhaving a drum which rotates to convey a sheet carried on the outercircumferential surface thereof; a plurality of inkjet heads each havingan ejection surface, which are aligned in a conveyance direction of thesheet so that the ejection surface of the each inkjet heads faces theouter circumferential surface of the drum; and a wiper for wiping theejection surface. In this inkjet printer, all the inkjet heads are fixedon a frame structure. The frame structure is moveable between a printingposition and a wiping position. The printing position is a positionwhere the frame structure is disposed when ink droplets are ejected froman ejection surface to a sheet conveyed by the conveyance mechanism. Thewiping position is such a position that the ejection surface is disposedfarther apart from the outer circumferential surface of the drum,compared to the printing position. At a time of printing, the wiper isin a standby position and faces no ejection surfaces, and the framestructure is positioned in the printing position. At a time of a wipingoperation, the frame structure moves to the wiping position. Then, thewiper moves in the circumferential direction of the drum, from thestandby position to an opposing position so as to face the ejectionsurface. Then, the wiper reciprocates in the axial direction of thedrum, thereby wiping the ejection surface.

SUMMARY OF THE INVENTION

In the above mentioned inkjet printer, however, the direction of thewiper moving from the standby position to the opposing position and themoving direction of the wiper at the time of wiping operation aredifferent. This necessitates a complicated mechanism for operating thewiper.

In view of the above problem, the present invention is made, and it isan object of the present invention to provide an inkjet recordingapparatus capable of wiping an ejection surface by means of a simplemechanism.

An inkjet recording apparatus of the present invention includes: a drum,a wiper, a plurality of inkjet heads, a head-moving mechanism, awiper-moving mechanism, and a control unit. The drum has a cylindricalouter circumferential surface, and rotates about a rotation axis thereofto convey a recording medium retained on the outer circumferentialsurface. The wiper is extended in an axial direction of the drum. Theinkjet heads are aligned in the circumferential direction of the drumalong the outer circumferential surface of the drum. Further, each ofthe inkjet heads has an ejection surface on which a plurality of nozzlesfor ejecting ink droplets are opened, the ejection surface beingextended in the axial direction and facing the outer circumferentialsurface. The head-moving mechanism moves the inkjet heads to any one ofpositions including a recording position and a wiping position. Therecording position is a position where inkjet heads are disposed at atime of forming an image on a recording medium on the outercircumferential surface by ejecting ink droplets from the nozzles to therecording medium, and the wiping position is such a position that theejection surface of each of the inkjet heads is farther distanced fromthe outer circumferential surface than in the recording position. Thewiper-moving mechanism moves the wiper in the circumferential directionalong the outer circumferential surface so as to wipe the ejectionsurface of at least one of the inkjet heads in the wiping position. Thecontrol unit which controls the wiper-moving mechanism so that theejection surface of the at least one of the inkjet heads is wiped whilethe inkjet heads are in the wiping position.

According to the present invention, the wiper wipes the ejection surfaceof at least one of the inkjet heads when moving in the circumferentialdirection along the outer circumferential surface of the drum. Thus, itis possible to wipe the ejection surface by means of a simple structurein which the wiper is not moved in the axial direction of the drum.

BRIEF DESCRIPTION OF THE DRAWINGS

Other and further objects, features and advantages of the invention willappear more fully from the following description taken in connectionwith the accompanying drawings in which:

FIG. 1 is a side view illustrating an embodiment of an inkjet printeraccording to the present invention.

FIG. 2 is a partial enlarged view of a cam illustrated in FIG. 1.

FIGS. 3A to 3D are diagrams each illustrating a positional relationbetween a projection of the cam and inkjet head.

FIG. 4 is a development view of a maintenance unit of FIG. 1 developedon a plane.

FIG. 5 to FIG. 9 are side views each illustrating a positional relationbetween an inkjet head and the maintenance unit, during each step of themaintenance operation taking place in the inkjet head illustrated inFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes, with reference to FIG. 1, an embodiment ofinkjet printer according to the present invention. An inkjet printer 1which is an inkjet recording apparatus is a color inkjet printer, andincludes: a sheet conveyance mechanism 20, four inkjet heads 2, ahead-moving mechanism 51, a maintenance unit 61; a maintenance unitmoving mechanism, and a control device 10. The sheet conveyancemechanism 20 includes a drum 21 having a cylindrical outercircumferential surface 21 a. The maintenance unit moving mechanismincludes a wiper-moving mechanism. The control device 10 serves as acontrol means which controls operations of the above mentioned members.In the lower part of the inkjet printer 1 is provided a sheet-feedingtray 11. On the top surface of the casing is provided a sheet receivingtray 12. Further, in the inkjet printer 1, a sheet conveyance path isformed. This sheet conveyance path extends from the sheet-feeding tray11 to the lower end of the drum 21, and from the lower end of the drum21 to the sheet receiving tray 12 via the upper end of the drum 21 alongthe outer circumferential surface 21 of the drum 21.

Each of the inkjet heads 2 has ink passages having nozzles for ejectingink droplets, and is formed in a parallelepiped shape elongated in theaxial direction of the drum 21. From each of these inkjet heads 2 isejected ink of one of the following four colors: magenta, yellow, cyan,and black. These four inkjet heads 2 are aligned in the circumferentialdirection of the drum 21 along the outer circumferential surfacethereof. In short, the inkjet printer 1 is a line printer.

The lower surface of each of the inkjet head 2 serves as an ejectionsurface 2 a having thereon nozzle openings. This ejection surface 2 a ofthe inkjet head 2 faces the outer circumferential surface 21 a. Each ofthe four inkjet heads 2 is disposed so that the normal to the center ofthe ejection surface 2 a is perpendicular to the outer circumferentialsurface 21 a.

The sheet-feeding tray 11 has a tray main body 13 opened in the upperdirection. In the tray main body 13 is stored a stack of sheets P.Inside the tray main body 13 are arranged a plate 14 which supports thesheets P from the bottom, and two springs 15 which urges the plate 14upward. The plate 14 is formed in a plane shape which is substantiallythe same as the tray main body 13, and is disposed in such a manner thatthe plate 14 is able to move upward or downward within the tray mainbody 13.

Further, the inkjet printer 1 includes a pickup roller 31 and a pickuproller moving mechanism 32 which rotates the pickup roller 31. Thepickup roller 31, while being rotated, contacts a sheet P at the top ofthe stack of sheets P so as to feed out the sheet P to the drum 21.

The pickup roller moving mechanism 32 includes a turning arm 33, a shaft34, and a not-illustrated drive motor. A lower end of the turning arm 33rotatably supports the pickup roller 31, and an upper end of the same isfixed to the shaft 34. The drive motor rotates the shaft 34 to rotatethe turning arm 33 about the shaft 34. With this pickup roller movingmechanism 32, the turning arm 33 is moved so that the pickup roller 31is positioned in one of the following two positions: a contact positionwhere the pickup roller 31 contacts the uppermost sheet P in the traymain body 13; and a separation position where the pickup roller 31 isapart from the uppermost sheet P in the tray main body 13. While thepickup roller 31 is in the separation position, the sheet-feeding tray11 is easily attached or detached. Note that aforementioned springs 15are structured in such a manner that a friction within a predeterminedrange is generated between the pickup roller 31 and the uppermost sheetP, irrespective of the number of sheets P stored in the tray main body13. This prevents a problem in feeding out a sheet P by the pickuproller 31.

Further, as a part of a sheet conveyance path, the inkjet printer 1includes an introduction path 41 through which a sheet P sent out fromthe sheet-feeding tray 11 by the pickup roller 31 is lead to the outercircumferential surface 21 a of the drum 21, which surface adsorbs andretains thereon the sheet P. The introduction path 41 is a substantiallystraight path which extends from the sheet-feeding tray 11 to the lowerend of the drum 21.

The drum 21 has a pipe-like shape and the axial direction thereofconforms with a direction perpendicular to the surface of the FIG. 1.The both ends of the drum 21 is closed. These closed ends support thedrum 21 so as to enable rotation of the drum 21 in the counter clockwisedirection on the FIG. 1. This rotation of the drum 21 in the counterclockwise direction is done by means of a not-illustrated drivemechanism including a conveyance motor. The rotation of the drum 21conveys a sheet adsorbed and retained on the outer circumferentialsurface 21 a along the outer circumferential surface 21 a of the drum21, in a conveyance direction A indicated by the arrow; that is, in thecircumferential direction of the drum 21.

The outer circumferential surface 21 a is formed on a circumferentialwall of the drum 21. This circumferential wall has through holes 22communicating an internal space 23 of the drum 21 with the outside ofthe drum. These through holes 22 are all uniformly formed. The drum 21is connected to a not-illustrated air-suction device which aspirates theair into the internal space 23. Driving of this air-suction deviceaspirates the external air into the internal space 23 via the throughholes 22, thus enabling adsorption of a sheet P on the outercircumferential surface 21 a of the drum 21.

As is understood from the above, the sheet conveyance mechanism 20includes the drum 21, the drive mechanism, and the air-suction device.Driving the air-suction device adsorbs and retains on the outercircumferential surface 21 a a sheet P having conveyed through theintroduction path 41 from the sheet-feeding tray 11. Further, driving ofthe drive mechanism rotates the drum 21 in the counter clockwisedirection, thereby conveying the sheet P in the conveyance direction A.Then, the inkjet heads 2 ejects ink of different colors to the sheet Pconveyed on the drum 21, while the respective ejection surfaces 2 a ofthe inkjet heads 2 face the sheet P. Thus, an intended colored image isprinted on the sheet P.

Towards the downstream of the drum 21 in the conveyance direction A isprovided a separator 45. The separator 45 separates a sheet P from theouter circumferential surface 21 a of the drum 21 retaining the sheet Pso as to feed the sheet P to an output path 43 which is also a part ofthe sheet conveyance path.

The head-moving mechanism 51 has four guide rails 52 and a cam 53 formedsubstantially in a shape of sector. Each of the guide rails 52 supportsone of the inkjet heads 2 so as to enable the supported inkjet head 2 tomove in a direction normal to the ejection surface 2 a. Each of theinkjet heads 2 is urged in a direction towards the outer circumferentialsurface 21 a by the gravity or a not-illustrated urging member. The cam53 is a plate in the shape of sector facing an end of the drum 21. Thecam 53 is capable of swinging about the rotational axis of the drum 21,in such a manner that the arched surface of the cam 53 moves in thecircumferential direction along the outer circumferential surface 21 aof the drum 21.

The cam 53 is swung by a not-illustrated positioning motor controlled bythe control device 10. Note that lines hidden by the cam 53 in FIG. 1are solid lines, though these lines should be dotted-lines. On thearched surface of the cam 53 are formed four projections 54 eachprojecting in the radial direction of the cam 53. These four projections54 are all formed in the same shape. On the other hand, each of theinkjet heads 2 has a boss 2 b projecting in the length directionthereof, on a side surface of the inkjet head 2 perpendicular to thelength direction of the inkjet head 2; that is, perpendicular to theaxial direction of the drum 21. The projections 54 on the cam 53 arepositioned so as to respectively face the bosses 2 b of the inkjet heads2. Each projection 54 abuts the boss 2 b of the corresponding inkjethead 2 to apply a force against the urging force applied to the inkjethead 2, thereby moving the inkjet head 2 in the direction departing fromthe outer circumferential surface 21 a. Thus, each inkjet head 2 movesalong the guide rail 52 in a direction normal to the ejection surface 2a.

The following details the projections 54 with reference to FIG. 2 andFIGS. 3A to 3D. FIG. 2 is a partial enlarged view of a cam 53. FIGS. 3Ato 3D are diagrams each illustrating a positional relation between aprojection 54 of the cam 53 and an inkjet head 2. As is understood fromFIG. 1 and FIG. 2, the outer peripheral edge of each of the projections54 is formed in a shape so that four abutting surfaces 54 a to 54 d areformed on the arched surface of the cam 53. The four abutting surfaces54 a to 54 d are parallel to the ejection surface 2 a, and arerespectively apart from the rotational axis of the drum 21 by differentdistances. More specifically, the four abutting surfaces 54 a to 54 dare formed so that distance from the rotational axis increases from themiddle left to the right of FIG. 2. Of these abutting surfaces 54 a to54 d, one abutting surface and an adjacent abutting surface are madecontinuous by a curved surface. The abutting surface 54 a is formedoutside the projection 54 on the arched surface of the cam 53.

As illustrated in FIG. 3A to 3D, the control device 10 controls theangular orientation of the cam 53, so as to change which one of theabutting surfaces 54 a to 54 d abuts the boss 2 b of the correspondinginkjet head 2. This varies the distance (hereinafter referred to asseparation distance) from the boss 2 b to the rotational axis of thedrum 21; i.e., the distance from the outer circumferential surface 21 aof the drum 21 to the ejection surface 2 a. Of these four bosses 2 b,two bosses 2 b next to each other are distanced from each other in thecircumferential directions by an amount equal to the distance in thecircumferential direction between two adjacent projections 54corresponding to the two bosses 2 b. The bosses 2 b of all the inkjetheads 2 therefore abut the same one of the abutting surfaces 54 a to 54d of the corresponding projections 54. As such, the separation distancesof all the inkjet heads 2 are the same. Thus, the four ejection surfaces2 a are aligned along the same circle with the rotational axis of thedrum 21 as its center, no matter which one of the abutting surfaces 54 ato 54 d abuts the corresponding boss 2 b.

As illustrated in FIG. 3A, when the abutting surface 54 a abuts thecorresponding boss 2 b, the inkjet head 2 is in the printing position orrecording position (see FIG. 1) for performing printing by ejecting inkdroplets from the nozzles of the inkjet head 2 towards the sheet P.

As illustrated in FIG. 3B, when the abutting surface 54 b abuts thecorresponding boss 2 b, the inkjet head 2 is in a capping position (SeeFIG. 7) in which each of later-mentioned caps 62 forms a sealed spacehaving the ejection surface 2 a as an inner-wall surface.

As illustrated in FIG. 3C, when the abutting surface 54 c abuts thecorresponding boss 2 b, the inkjet head 2 is in the wiping position (SeeFIG. 8) in which the ejection surface 2 a contacts a portion nearby aleading end of a later-mentioned wiper 63.

As illustrated in FIG. 3D, when the abutting surface 54 d abuts the boss2 b, the inkjet head 2 is in a retracted position (See FIG. 5) in whichthe ejection surface 2 a separates from the leading end of the wiper 63.The separation distances of the inkjet heads 2 in the above mentionedpositions are such that: separation distance of the inkjet heads 2 inthe printing position <separation distance of the same in the cappingposition <separation distance of the same in the wiping position<separation distance of the same in the retracted position.

The following describes the maintenance unit 61 with reference to FIG. 1and FIG. 4. FIG. 4 is a development view illustrating a maintenance unitof FIG. 1 developed on a plane. As illustrated in FIG. 1 and FIG. 4, themaintenance unit 61 performs a maintenance of the ejection surfaces 2 aof the inkjet heads 2, and includes: four caps 62 aligned in theconveyance direction A of the sheet P, four wipers 63 aligned in theconveyance direction A of the sheet P, a maintenance tray 64 supportingthe caps 62 and wipers 63, a waste liquid tray 71, and a waste liquidtank 72.

Each of the caps 62 is made of an elastic material such as anink-resistance rubber or resin. The each of the caps 62 has an annularprojection having a substantially rectangular plane shape, whichprojection defines a recessed portion whose bottom surface is themaintenance tray 64. The recessed portion defined by the annularprojection extends in the axial direction of the drum 21 in a planeview. The size of the recessed portion is smaller than the ejectionsurface 2 a, but is sufficient for including the entire region of theejection surface 2 a where the nozzle openings are provided. While thecaps 62 faces the ejection surfaces 2 a and while the inkjet heads 2 arein the capping position, the annular projection of each of the caps 62and the corresponding ejection surface 2 a are closely attached, therebyforming a sealed space having the ejection surface 2 a as an inner-wallsurface. This restrains drying and thickening of the ink inside thenozzles. Further, through a purging operation for discharging thickenedink inside the nozzles, the ink ejected from the ejection surface 2 a isreceived inside the cap 62 while avoiding dispersion of ink dropletsoutside the cap 62.

Each of the wipers 63 is a blade for wiping the ejection surface 2 a,and is made of an elastic material such as an ink-resistant rubber orresin. The four wipers 63 all have the same size. Further, the wipers 63is provided perpendicularly to the outer circumferential surface 21 a ofthe drum 21, and extends in the axial direction of the drum 21. Each ofthe four wipers 63 is longer than the ejection surface 2 a in the axialdirection of the drum 21. The leading ends of the four wipers 63 may bepositioned along a circle M along which the four ejection surfaces 2 aof the inkjet heads 2 are aligned when the inkjet heads 2 are in thewiping position. Note, however, that the present embodiment deals with acase where the leading ends of the wipers 63 are positioned so as toslightly exceed from the circle M (See FIG. 8). An amount of each wiperexceeding from the circle M is designed so that the wiper 63 is capableof wiping the entire region of the ejection surface 2 a.

The maintenance tray 64 is formed substantially in the shape of sector,and includes a curved part and a plane part connected to the curvedpart. The curved part faces the outer circumferential surface 21 a ofthe drum 21, and is curved along the outer circumferential surface 21 aof the drum 21. The plane part faces an end surface of the drum 21, andis capable of swinging about the rotational axis of the drum 21 so as tomove the curved part in the circumferential direction of the outercircumferential surface 21 a of the drum 21. The maintenance tray 64 isswung by a not-illustrated maintenance motor controlled by the controldevice 10. Note that lines hidden by the maintenance tray 64 in FIG. 1are solid lines, though these lines should be dotted-lines. The outersurface of the curved part of the maintenance tray 64 holds the fourwipers 63 and the four caps 62, in such a manner that the wipers 63 andthe caps 62 are alternately positioned on the surface in the conveyancedirection A of the sheet P. One of the wipers 63 is paired with anadjacent one of the caps 62, and a single pair of the wiper 63 and cap62 corresponds to a single inkjet head 2. Further, in each pair, thewiper 63 is positioned upstream of the cap 62 in the conveyancedirection A.

The control device 10 controls the angular orientation of themaintenance tray 64 to move the wipers 63 and caps 62 between thestandby position and the opposing position (preparation position) alongthe outer circumferential surface 21 a of the drum 21. The standbyposition is a position which is upstream from the four inkjet heads 2 inthe conveyance direction A, and is a position where the maintenance tray64 faces none of the ejection surfaces 2 a. In other words, the standbyposition is a position where the maintenance tray 64 does not face anarea including the four ejection surfaces 2 a. The opposing position isa position where the maintenance tray 64 faces all the ejection surfaces2 a. While the wipers 63 and caps 62 are in the opposing position, eachof the caps 62 faces the corresponding ejection surface 2 a of thecorresponding inkjet head 2. Further, while the wipers 63 and the caps62 are in the standby position, the openings of the recessed portions ofall the caps 62 are faced downward. Thus, waste ink stored in the caps62 from the caps 62 due to its own weight. In the present embodiment,the maintenance tray 64 and the maintenance motor or the like, form amaintenance unit moving mechanism including the wiper-moving mechanism.

The waste liquid tray 71 is positioned so as to be located below thecaps 62 while the caps 62 are in the standby position. This waste liquidtray 71 leads, to the waste liquid tank 72, the waste ink dischargedfrom the caps 62 in the standby position. The waste liquid tank 72 ispositioned below the waste liquid tray 71, and stores therein the wasteink having lead by the waste liquid tray 71.

Next, the following describes an operation which takes place at a timeof performing printing to the sheet P. It is supposed that the inkjetheads 2 are brought to the printing position prior to the printing.First, a sheet P is fed to the drum 21 from the sheet-feeding tray 11.In this step, the uppermost sheet P among a stack of sheets P stored inthe sheet-feeding tray 11 contacts the pickup roller 31. The pickuproller 31 rotates counter clockwise while being in contact with thesheet P, thereby feeding the sheet P to the introduction path 41. Thesheet P fed out is then lead through the introduction path 41, andarrives at the drum 21.

At the same time, the drive mechanism drives the drum 21 to rotate thedrum 21 in the conveyance direction A, and the air-suction device isdriven to adsorb and retain the sheet P on the outer circumferentialsurface 21 a of the drum 21. The sheet P retained on the outercircumferential surface 21 a of the drum 21 is then conveyed in theconveyance direction A with the rotation of the drum 21.

When the sheet P reaches a position so as to face the ejection surface 2a, the ejection surfaces 2 a of the four inkjet heads 2 eject ink fromtheir nozzles to form an image on the sheet P. Then, the sheet P onwhich the image is formed is separated from the outer circumferentialsurface 21 a of the drum 21 by the separator 45, and is fed out to theoutput path 43. The sheet P fed to the output path 43 is conveyedtowards the sheet receiving tray 12, and is received by the sheetreceiving tray 12.

Next, the following details with reference to FIG. 5 to FIG. 9 amaintenance operation of the inkjet heads 2. The maintenance operationof the inkjet heads 2 includes: a process of discharging thickened inkinside the nozzle openings on the ejection surfaces 2 a, and a processof shaping meniscus of ink formed on each of the nozzle openings. Themaintenance operation is performed at a time of powering on the inkjetprinter 1, or immediately before the printing to a sheet P.

FIG. 1 illustrates an ordinary state where printing to the sheet P ispossible. During this state, each of the inkjet heads 2 is in theprinting position, and the boss 2 b of the inkjet head 2 abuts theabutting surface 54 a of the corresponding one of projections 54.Further, the wipers 63 and caps 62 are in standby position. When themaintenance operation starts during this state, the control device 10controls the angular orientation of the cam 53 so that the boss 2 b ofeach of the inkjet heads 2 abuts the abutting surface 54 d. Thus, theinkjet heads 2 move from the printing position to the retractedposition, as illustrated in FIG. 5.

Then, the control device 10 controls the angular orientation of themaintenance tray 64 to move the wipers 63 and caps 62 from the standbyposition to the opposing position, as illustrated in FIG. 6. Thus, eachof the caps 62 faces corresponding one of the ejection surfaces 2 a.Each of the wipers 63 on the other hand is positioned slightlydownstream from the corresponding one of the ejection surfaces 2 a inthe conveyance direction A. In other words, each of the wipers 53 movesfrom the standby position to the opposite side of the corresponding oneof the ejection surfaces 2 a.

Further, the control device 10 controls the angular orientation of thecam 53 so that the boss 2 b of each of the inkjet heads 2 abuts theabutting surface 54 b. This moves the inkjet head 2 from the retractedposition to the capping position, as illustrated in FIG. 7. As a result,the ejection surface 2 a and the annular projection of the cap 62 areclosely attached to each other, forming a sealed space having theejection surface 2 a as an inner-wall surfaces. Further, a purgingoperation for discharging the thickened ink in the nozzles and the airinside the inkjet head 2 is performed under the control of the controldevice 10. The purging operation is performed by driving anot-illustrated pomp connected to the ink supply path of the inkjet head2. At this point the ink ejected from the ejection surface 2 a isreceived in the cap 62.

When the purging operation is completed, the control device 10 controlsthe angular orientation of the cam 53 so that the boss 2 b of each ofthe inkjet heads 2 abuts the abutting surface 54 c. Thus, the inkjethead 2 moves from the capping position to the wiping position asillustrated in FIG. 8.

Then, as illustrated in FIG. 9, the control device 10 controls theangular orientation of the maintenance tray 64 to move the wiper 63 andthe cap 62 in a direction from the opposing position to the standbyposition so that each wiper 63 passes only one of the ejection surfaces2 a corresponding to the wiper 63. In other words, the control device 10controls the angular orientation of the maintenance tray 64 to move thewiper 63 and the cap 62 in a reverse conveyance direction B indicated bythe arrow so that each wiper 63 moves from the opposing position to theopposite side of the corresponding one of the ejection surfaces 2 a.During this state, the leading ends of the four wipers 63 are positionedso as to slightly exceeds the circle M along which the ejection surfaces2 a of the four heads 2 in the wiping position are aligned. Thus, eachof the wipers 63 moves in the reverse conveyance direction B, whilebeing in contact with the corresponding one of the ejection surfaces 2a. This allows the wipers 63 to wipe the entire ejection surfaces 2 a,respectively. Thus, shaping of meniscus to be formed at each of thenozzle openings is possible.

Then, the control device 10 controls the angular orientation of the cam53 so that the boss 2 b of each of the inkjet heads 2 abuts the abuttingsurface 54 d. This moves the inkjet heads 2 from the wiping position tothe retracted position. The control device 10 further controls theangular orientation of the maintenance tray 64 so that the wipers 63 andcaps 62 move to the standby position in the reverse conveyance directionB. Then, waste ink in the caps 62 in the standby position is dischargedtherefrom to the waste liquid tray 71. The discharged waste ink is thenlead to the waste liquid tank 72 through the waste liquid tray 71.

Then, the control device 10 controls the angular orientation of the cam53 so that the boss 2 b of each of the inkjet heads 2 abuts the abuttingsurface 54 a. This moves the inkjet heads 2 from the retracted positionto the printing position as illustrated in FIG. 1, and the maintenanceoperation of the inkjet heads 2 is completed.

According to the above detailed embodiment, the wiper 63 wipescorresponding one of the ejection surfaces 2 a while moving in thecircumferential direction along the outer circumferential surface 21 aof the drum 21. Therefore, wiping of the ejection surface 2 a ispossible with a simple structure in which the wipers 63 are not moved inthe axial direction of the drum 21.

For each of the inkjet heads 2 in the printer 1 of the presentembodiment, the normal of the ejection surface 2 a is perpendicular tothe outer circumferential surface 21 a, and the separation distances ofall the inkjet heads 2 are the same whether all the inkjet heads 2 arein the printing position or in the wiping position. Thus, unevenness inthe contact strength of wipers 63 made of an elastic material to theejection surfaces 2 a, which occurs within the four ejection surfaces 2a, is made extremely insignificant. As a result, all four ejectionsurfaces 2 a are evenly wiped entirely.

Further, the head-moving mechanism 51 is able to move the inkjet heads 2by means of a simple structure adopting four guide rails 52 and a singlecam 53. Adoption of such a structure in which the cam 53 swing about therotational axis of the drum 21 allows a simple structure of thehead-moving mechanism 51.

Further, the maintenance unit 61 has four wipers 63, the number of whichcorresponds to the number of the inkjet heads 2. The four wipers 63 arealigned in the circumferential direction along the outer circumferentialsurface of the drum 21. During the maintenance operation, the fourwipers 63 respectively wipes corresponding ejection surfaces 2 a.Therefore, contamination of ink on the ejection surface 2 a isprevented.

In addition, the inkjet heads 2 are moveable to the retracted positionby means of the head-moving mechanism, which enables the wipers 63 tomove without contacting the ejection surfaces 2 a. This restrains damageto meniscus formed on each nozzle opening.

Note that in the above embodiment, each of the inkjet heads 2 arepositioned so that the normal of the ejection surface 2 a isperpendicular to the outer circumferential surface 21 a, and that theseparation distances of all the inkjet heads 2 are the same whether allthe inkjet heads 2 are in the printing position or in the wipingposition. However, the normal of the ejection surface 2 a of each head 2does not necessarily have to be perpendicular to the outercircumferential surface 21 a. Further, the separation distances of allfour inkjet heads 2 do not have to be the same. Further, the head-movingmechanism 51 may move the four heads 2 in a direction slanted inrelation to the normal of the ejection surfaces 2 a.

The above embodiment deals with a case where the maintenance unit 61includes four wipers 63, and the four wipers 63 wipe the correspondingejection surfaces 2 a during the maintenance operation, respectively.However, it is possible to adopt a maintenance unit 61 having a singlewiper which wipes all four ejection surfaces 2 a. Alternatively, it isalso possible to adopt a maintenance unit 61 having two wipers each ofwhich wipes two of the ejection surfaces 2 a.

Further, in the above embodiment, the inkjet heads 2 are moved byswinging the cam 53 about the rotational axis of the drum 21. However,other structures are possible for moving the inkjet heads 2. Forexample, the inkjet heads may be moved independently from the others, bymeans of a linear actuator. Alternatively, a cam may be provided foreach of the heads. Note that the four heads 21 do not necessarily haveto move simultaneously.

Further, the above embodiment allows the inkjet heads 2 to be moved tothe retracted position. However, a structure which does not move theinkjet heads 2 to the retracted position is also possible. In such acase, the inkjet heads 2 are moved to the wiping position, instead ofthe retracted position. Note, however, that the ejection surfaces 2 aare wiped even when the wiping operation is not necessary.

Further, the above embodiment deals with a case where, during themaintenance operation, the wipers 63 moves from the standby position tothe opposing position in the conveyance direction A, and then wipes thecorresponding ejection surfaces 2 a while moving back in the reverseconveyance direction B. However, the wipers 63 may wipe thecorresponding ejection surfaces 2 a while moving in the conveyancedirection A.

Further, the above embodiment deals with a case where the caps 62receives the ejected ink droplets. However, these caps may be omitted.Instead, a purge area capable of retaining ink to a predeterminedposition of the outer circumferential surface 21 of the drum 21 may beprovided, and ink droplets may be ejected to the purge area during thepurging operation. This allows omission of the process of forming withthe cap 62 a sealed space having the ejection surface 2 a as aninner-wall surface. As a result, the maintenance operation is promptlycompleted. In this case, the wiper 63 is moved only between the opposingposition as illustrated in FIG. 8 and the position illustrated in FIG.9; that is, a position on the opposite side of the ejection surface 2 aacross from the opposing position.

Further, in the above case, it is also possible to adopt a structure inwhich the wipers 63 wipes the corresponding ejection surfaces 2 a whenthe wipers 63 moves in the conveyance direction A and in the reverseconveyance direction B. In the maintenance operation, the inkjet heads 2may be moved to the wiping position after the purging operationperformed with the inkjet heads 2 in the printing position, and thenwipe the ejection surfaces 2 a in the wiping position with the wipers63. After the wiping is completed, the wipers 63 may be kept in the sameposition, and the inkjet heads 2 may be moved to the printing positionto complete the maintenance operation. In this case, the wipers 63 aremoved to the opposite direction to wipe the ejection surfaces 2 a in thenext wiping operation performed after the purging operation. This allowsfurther promptness of the maintenance operation.

Further, the above embodiment deals with a case where a sheet P is heldon the outer circumferential surface of the drum 21 by means of theair-suction device. However, the outer circumferential surface of thedrum 21 may posses adhesiveness. This simplifies the structure of thedevice.

While this invention has been described in conjunction with the specificembodiments outlined above, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart. Accordingly, the preferred embodiments of the invention as setforth above are intended to be illustrative, not limiting. Variouschanges may be made without departing from the spirit and scope of theinvention as defined in the following claims.

What is claimed is:
 1. An inkjet recording apparatus, comprising: a drumhaving a cylindrical outer circumferential surface, which rotates abouta rotation axis thereof to convey a recording medium retained on theouter circumferential surface; a wiper extended in an axial direction ofthe drum; a plurality of inkjet heads aligned in the circumferentialdirection of the drum along the outer circumferential surface of thedrum, wherein each of the inkjet heads has an ejection surface on whicha plurality of nozzles for ejecting ink droplets are opened, theejection surface being extended in the axial direction and facing theouter circumferential surface; a head-moving mechanism which moves theinkjet heads to any one of positions including a recording position anda wiping position, wherein the recording position is a position whereinkjet heads are disposed at a time of forming an image on a recordingmedium on the outer circumferential surface by ejecting ink dropletsfrom the nozzles to the recording medium, and the wiping position issuch a position that the ejection surface of each of the inkjet heads isfarther distanced from the outer circumferential surface than in therecording position; a wiper-moving mechanism which moves the wiper inthe circumferential direction along the outer circumferential surface soas to wipe the ejection surface of at least one of the inkjet heads inthe wiping position; and a control unit which controls the wiper-movingmechanism so that the ejection surface of the at least one of the inkjetheads is wiped by the wiper moving in the circumferential directionwhile the inkjet heads are in the wiping position.
 2. The apparatusaccording to claim 1, wherein the inkjet heads are disposed so that anormal direction of the ejection surface of each of the inkjet heads isperpendicular to the outer circumferential surface, and that ejectionsurfaces of all the inkjet heads are apart from the outercircumferential surface by the same distance whether all the inkjetheads are in the recording position or in the wiping position.
 3. Theapparatus according to claim 2, wherein: the head-moving mechanismincludes guide rails supporting the inkjet heads so as to enable each ofthe inkjet heads to move in a direction normal to the ejection surfacethereof, and a cam which moves the inkjet heads by contacting the inkjetheads.
 4. The apparatus according to claim 3, wherein the cam moves theinkjet heads by swinging about the rotational axis of the drum.
 5. Theapparatus according to claim 1, wherein: the number of wipers and thatof the inkjet heads are the same, and a plurality of the wipers arealigned in the circumferential direction along the outer circumferentialsurface; the wiper-moving mechanism moves the plurality of the wipers;and the control unit controls the wiper-moving mechanism so that theplurality of the wipers respectively wipe the inkjet heads while theinkjet heads are in the wiping position.
 6. The apparatus according toclaim 1, wherein the head-moving mechanism is capable of moving theinkjet heads to a retracted position so that the ejection surface ofeach of the inkjet heads in the retracted position is farther distancedfrom the outer circumferential surface than in the wiping position, andthat, when the wiper moved by the wiper-moving mechanism is in aposition to face the ejection surface of any one of the inkjet heads,the wiper is apart from the inkjet head.
 7. The apparatus according toclaim 1, wherein the wiper-moving mechanism is configured to move thewiper between a standby position and a preparation position in thecircumferential direction along the outer circumferential surface,wherein the standby position is a position at which the wiper is outsideof an area including the ejection surface and the preparation positionis a position at which the wiper faces the ejection surface of at leastone of the inkjet heads in the standby position; and the wiper isconfigured to wipe the ejection surface of the at least one of theinkjet heads in the wiping position when the wiper moves between thestandby position and the preparation position.
 8. The apparatusaccording to claim 1, wherein the wiper has a length greater than alength of the ejection surface in the axial direction.
 9. An inkjetrecording apparatus, comprising: a drum having a cylindrical outercircumferential surface, which rotates about a rotation axis thereof toconvey a recording medium retained on the outer circumferential surface;a maintenance unit comprising a wiper and a cap both extending in anaxial direction of the drum; a plurality of inkjet heads aligned in thecircumferential direction of the drum along the outer circumferentialsurface of the drum, wherein each of the inkjet heads has an ejectionsurface on which a plurality of nozzles for ejecting ink droplets areopened, the ejection surface being extended in the axial direction andfacing the outer circumferential surface; a head-moving mechanism whichmoves the inkjet heads to any one of positions including a recordingposition, a wiping position, and a capping position, wherein therecording position is a position where inkjet heads are disposed at atime of forming an image on a recording medium on the outercircumferential surface by ejecting ink droplets from the nozzles to therecording medium, and the wiping position is such a position that theejection surface of each of the inkjet heads is farther distanced fromthe outer circumferential surface than in the recording position, andthe capping position is a position at which the ejection surface of eachof the inkjet heads is closer to the outer circumferential surface thanthe wiping position and is farther from the outer circumferentialsurface than the recording position; a maintenance unit moving mechanismwhich moves the wiper and the cap in the circumferential direction alongthe outer circumferential surface so as to wipe the ejection surface ofat least one of the inkjet heads in the wiping position; and controlmeans for controlling the maintenance unit moving mechanism so that theejection surface of the at least one of the inkjet heads is wiped whilethe inkjet heads are in the wiping position, wherein, after theplurality of inkjet heads move from the capping position, at which thecap forms a sealed space having the ejection surface as an inner-wallsurface, to the wiping position, the wiper moves to pass only one of theejection surfaces such that the ejection surface is wiped by the wiper.